Spot welding cap changer

ABSTRACT

The invention relates to a spot welding cap changer ( 1 ) with a cap puller ( 2 ) and two cap magazines ( 3, 3 A), the cap puller ( 2 ) having a gripper ( 20 ) with spring-loaded, pivotable jaws ( 21, 22 ), which in response to a turning and axial pulling-off movement detaches a spot welding cap (K) of a pincer spot welding head introduced into it from a shaft of the pincer welding head in such a way that it is clamped to prevent it twisting, and the cap magazines ( 3, 3 A) holding spot welding caps respectively in a round cap carrier ( 31 ) such that they are circularly arranged in a directed and oriented manner and are respectively transported individually one after the other into an access position against a stop ( 32 ) by an advancing force (P).

The invention relates to a spot welding cap changer with a cap extractorand two cap magazines, the cap extractor having a gripper withspring-loaded, pivoting jaws, which in response to a turning and axialextraction movement detaches a spot welding cap of a pincer spot weldinghead inserted into it from a shaft of the pincer welding head in such away that it is clamped to prevent twisting, and the cap magazinesholding spot-welding caps in a cap carrier in such a way that they arecircularly arranged in a directed and oriented manner and are one by onetransported by an advancing force against a stop, into an accessposition allowing to attach them axially to the free shaft of the pincerand to extract them with it.

Such a mechanical electrode cap changer is known from the DE 102 22 248A1. It has a two-part cap extractor, accessible from both sides, in abody separate from the magazine.

Since gravity causes the caps to slide against a cap stop, the devicecan only be operated stationary in the vicinity of a mobile weldingrobot. Changing caps at a stationary pincer spot welding head, to whicheach component is fed by a robot for welding, is therefore not possible.The pincer spot welding heads/welding installations often have shortshafts, which are for instance curved, so that the cap extractor,equipped with three large jaws and accordingly big, cannot be positionedfor extraction.

It is the object of the invention to provide for an automatic faster andsafer exchange of the spot welding caps both at mobile and stationaryspot welding installations with a short access distance.

The solution resides in that the cap extractor has two opposed grippers,each with jaws that are open at their ends and can be rotated towardseach other with approximately parallel toothed grip surfaces whosedistance is slightly smaller than a diameter of a spot welding cap, andeach cap magazine contains a cap carrier, which, driven by a spring box,presses by way of its advancing force one of the caps respectivelyagainst the stop, and in the access position a rim overlap overlaps thecap on one side.

Advantageous forms of the invention are indicated in the subclaims.

In the new embodiment the cap extractor and the magazine are mounted ona support which preferably is spring-mounted. In contrast to the knownsystem, the new construction design gives the possibility not only to beused at welding robots, but also at stationary pincer welding heads orwelding installations.

Compared with the known clamping system with three jaws, the newcap-extraction installation provides for shorter clamp and spin travels,therefore much shorter intervals for detaching the caps. Moreover, fromthe smaller design results a wider array of application, for instance atnon-standard pincers or very short, curved shafts.

The two cap extractors are each open at the ends of the jaws and thusaccessible to a cap. The jaws grip it directly by way of the undersizeof their distance and detach the cap, whereby a rotation around an angleof about 30-60° suffices. This way a cap change is possible even inextremely narrow confines. Since the two grippers are oriented inopposite directions, respectively one of them is accessible from thevarious sides in a clockwise rotation, so that no turning of the pinceris necessary, even if the pincer shafts are screwed on.

Furthermore, the round magazine is much more compact than the straightmagazine functioning by gravity of the known installation. It can beheld and operated in any position because of the spring drive.

Furthermore, the two round magazines arranged on parallel axes providein each case for an access with short radial travel to the accesspositions in the access openings. In an embodiment with a magazinecover, this cover is directly shifted during access, far enough to letthe rim overlap uncover the cap frame, so that the detaching ispossible. The example shows a radial infeed and an axial access of theshafts into the magazine.

Both partial devices, the cap changer, and the cap magazine, are mountedon a support close to one another, and thus can be set up stationary, ormounted to a robot arm in a fixed or detachable manner. In the firstcase the welding robot changes the caps of its own pincer, and in thesecond case the robot changes the caps at the stationary pincers orinstallations respectively by means of the device. The changing deviceat the robot arm is movably mounted, constantly ready for operation in afree space next to the gripper of the robot or on a guide rail, or it islocated in a parking position, where it can be picked up and brought tooperation by the gripper; this is called alternating pincer principle.

Advantageously, cap sensors are arranged on the device., which indicatewhether a cap is in place or not. Moreover, the charging level of themagazines is monitored. This way it is ensured that after a cap change acap is in place at the shaft of the pincer welding head before thecooling water is switched on. Furthermore it can be verified, whetherthe old cap was removed, when it is reported that there is no cap inplace while the shaft is approaching.

The embodiment of the cap magazine without a cover holds the weldingcaps in an elastic cap carrier in a close fit, axially movable bypropulsive or tractive force.

Advantageous embodiments are represented in the FIGS. 1 to 6.

FIG. 1 shows the entire device schematically and in perspective;

FIG. 2 shows a transparent top view of the cap extractor;

FIGS. 2A, 2B show detailed enlargements of the grip surfaces;

FIG. 3 shows a perspective of the cap extractor;

FIG. 4 shows a cap magazine in perspective, closed, enlarged

FIG. 5 shows a cap magazine in perspective, open, enlarged

FIG. 6 shows a top view of the magazine cover.

FIG. 1 shows a complete spot welding cap changer 1, which is movablyheld on a support rail 5 at a robot arm. Alternatively, it is firmlymounted with the mounting plate 50. The bilaterally equipped capextractor 2 is bolted at the free end of the mounting plate 50, with thetwo grippers 20 respectively on the sides, their direction opposite toone another. Pulled off caps K are depicted between the jaws 21, 22,after being detached at the rim of a storage container they drop intoit.

Offset to the rear from the cap extractor 2 respectively one capmagazine 3, 3A laterally offset to the other is mounted on the mountingplate 50, with the magazine cover 4 respectively directed laterally andthe access openings 40 oriented axially parallel to the extractedwelding caps K that are still held by the gripper, so that the shafts ofthe pincer spot welding head have to travel only short distances whilechanging the caps.

FIG. 2 shows a top view on the cap extractor 2, which consists of veryfew parts. The grippers 20 are composed of one fixed, toothed jaw 21respectively, and one jaw 22 which is mounted in such a way that it canbe pivoted towards said jaw 21. The pivot joint 24 is located behind thefixed jaw 21 by way of a U-shaped structure of the movable jaw arm 25,so that a cap K positioned in the gripper 20 will be clamped at a twistdepending on the direction of rotation.

The initial pressing force of the jaws 21, 22 is caused by a bracingspring 26, which for example, is formed as a spiral or bracing springwith spread ends, each pressing against a jaw arm 25.

On the infeed side the grippers 20 are provided with infeed skews 27,28. From these extend the roughly parallel grip surfaces 23, each with atoothing in opposite direction 29A, 29B, as FIGS. 2A and 2B show inpartial view and in detail. If there is no cap K inserted in thegrippers 20, then the distance A of the grip surfaces 23 has a minorundersize compared to the cap outside diameter D.

FIG. 3 shows that the spring 26 and the movable jaws 21, 22 as well as ajaw plate 62, on which the fixed jaws 21 are formed, are held betweentwo cover plates 60, 61. The jaw plate 62 has a corresponding cavity, inwhich the U-shaped jaw arms 22 have free space to move.

FIG. 4 shows a round cap magazine 3, which consists of a barrel shapedcap carrier 31, closed with a magazine cover 4, whereas a radial sectionremains free up to the rounded access opening 40, in which a welding capK in the withdrawal position is pressed to the edge of a stop 32 at thecover.

The cover 4 has a small rim overlap 41 of the cap frame in the curve ofthe access opening 40, an induct skew 42 connecting to said rim overlapwhich is cascaded to the top side of the cover. At an embodiment with ahinged cover 4, a slot 43 is formed, through which reaches a bracket 34,bevelled on the outside, which keeps the cover 30 shut.

On the other side of the access opening 40 a hinge 44 with a slottedhole 45 is formed in the extension level of the cover, the cones 46 ofsaid hinge being held in a hinge support 47.

FIG. 5 shows the open round magazine 3 with a hinge and equipped with awelding cap K in the drill holes 30 of the cap carrier 31, the cap Kprotruding by a few millimetres. A firmly mounted spring box 33,schematically depicted, is in the centre of the cap carrier 31, saidspring box carrying the bracket 34 so that it can be radially moved. Apreloaded spindle or spiral spring is arranged centrally in the springbox 33, one end of the spring being fixed to the spring box 33, theother to the cap carrier 31, so that the latter is pressed with atorsion force P in the direction of the stop 32, which extends radiallyon the magazine cover.

The plate-shape bracket 34 extends in a diagonal guiding slot on thecover of the spring box 33. In the closed state, as shown here, acompression spring arrangement 35, held in the cover, extends from thebracket 34 and is supported by means of a support pin 36 on the roundedhinge support 47, and presses the bracket 34 in the closed position, inwhich it overlaps the cover 4 in the closed state and holds the rimoverlap 41 in the overlap position, the cone 46 being in the rear stopposition in the slotted hole 45, as FIG. 1 shows. To open the cover 4,the bracket 34 is pushed back manually. Alternatively, the roundmagazine can be implemented without a hinge for the opening of thecover. In this case the cover is only held in a movable manner, so thatthe shaft of the pincer, when inserted, slides the cover by the skew 42to release the rim overlap.

FIG. 6 shows a top view on the magazine cover 4, whose main outlineconsists of two semi-circles with shifted centres M1, M2, whereby on oneside the access opening 40 extends in the direction of the centre, andon the opposite side the hinge 44 extends on the outside. The slot inthe cover 43 extends 4 in the central area in the direction between theaccess opening 40 and the hinge 44. The bracket 34 in the cover and inthe fixed spring box 33 is guided in this direction. The cover 4 isabout 15 mm high and largely hollow shaped and has a stiffening coverrim 48, which passes into the stop 32 and on the other side into thehinge 44. The cover 4 is lowered at the induct skew 42 by about 5 mm tothe infeed area. Internally, the cover surface drives the caps to thewithdrawal level when turned in the stop position. A chamber 49, whichcontains the compression spring arrangement 35, is represented with adashed outline.

The compact construction of the cap extractor with the magazines allowsfor a significant reduction of the changing times, for example, from 22to 17 sec, which corresponds to about 23%.

LIST OF REFERENCE SIGNS

1 spot welding cap changer

2 cap extractor

20 gripper

21, 22 jaws

23 grip surfaces

24 pivot joint

25 jaw arm

26 bracing spring

27, 28 infeed skews

29A, 29B toothing

3, 3A cap magazine

30 drill holes

31 cap carriers

32 stop

33 spring box

34 bracket

35 compression spring

36 support pin

4 magazine cover

40 access opening

41 rim overlap

42 induct skew on the cover

43 slot in the cover

44 hinge

45 slotted hole in the hinge

46 cones

47 hinge support

48 cover rim

49 compression spring chamber

5 support rail

50 mounting plates

60, 61 cover plates

62 jaw plate

A gripping jaw distance

D outside diameter of the caps

K cap

P advancing force

M1, M2 semicircle, centres

1. Spot welding cap changer (1) with a cap extractor (2) and two capmagazines (3, 3A), the cap extractor (2) having a gripper (20) withspring-loaded, pivoting jaws (21, 22) which in response to a turning andaxial extraction movement detaches a spot welding cap (K) of a pincerspot welding head inserted into it from a shaft of the pincer weldinghead in such a way that it is clamped to prevent it twisting, and thecap magazines (3, 3A) holding spot welding caps respectively in a capcarrier (31) in such a way that they are circularly arranged in adirected and oriented manner and are one by one transported by anadvancing force (P) against a stop (32), into an access positionallowing to attach them axially to the free shaft of the pincer and toextract them with it, characterized in that the cap extractor (2) hastwo opposed grippers (20), each with jaws (21, 22) that are open attheir ends and can be rotated towards each other with approximatelyparallel toothed grip surfaces (23) whose distance (A) is slightlysmaller than a diameter of a spot welding cap (DK), and each capmagazine (3, 3A) contains a cap carrier (31) which, driven by a springbox (33), presses by way its advancing force (P) one of the caps (K)respectively against the stop, and in the access position a rim overlap(41) overlaps the cap (K) on one side.
 2. Spot welding cap changeraccording to claim 1, characterized in that respectively one of the jaws(21) of the corresponding gripper (20) is fixed at a jaw plate, and thecorresponding movable jaw (22) is formed at an U-shaped jaw arm (25),which is supported with a pivot joint (24) behind the fixed jaw (21). 3.Spot welding cap changer according to claim 2, characterized in thatbetween the two movable jaw arms (25), a preloaded bracing spring (26)is mounted.
 4. Spot welding cap changer according to claim 1,characterized in that the jaws (21, 22) have infeed skews (27, 28). 5.Spot welding cap changer according to claim 4, characterized in that thegrip surfaces (23) in each case have an asymmetric toothing (29A, 29B),which on the two parallel jaws (21, 22) is oriented in oppositedirections.
 6. Spot welding cap changer according to claim 3,characterized in that the jaw arms (25), the bracing spring (26) and thejaw plate (62) are held between cover plates (60, 61).
 7. Spot weldingcap changer according to claim 1, characterized in that the spring box(33) contains a spiral or coil spring, one end of which is fixed at thespring box (33), and the other end of which is fixed at the cap carrier(31).
 8. Spot welding cap changer according to claim 1, characterized inthat a magazine cover (4) is held preloaded by a spring (35) in thedirection of the access opening (40) so that the rim overlap (41)overlaps a cap frame in its stop position.
 9. Spot welding cap changeraccording to claim 8, characterized in that a bracket (34) isspring-loaded and movably held at the spring box (33), said bracketreaching through the closed magazine cover (4) and, by overlapping it,holding it in place.
 10. Spot welding cap changer according to claim 8,characterized in that the magazine cover (4) is articulated at a hingesupport (47), situated opposite of the access opening (40).
 11. Spotwelding cap changer according to claim 10, characterized in that themagazine cover (4) is movably guided in a slotted hole (45) on the hingesupport (47).
 12. Spot welding cap changer according to claim 1,characterized in that the magazine cover (4) bears a stiffening coverrim (48), which on one side forms the rim overlap (41) and on the otherside forms a hinge (44).
 13. Spot welding cap changer according to claim1, characterized in that the cap extractor (2) with grippers (20)projecting at its front side is mounted on a mounting plate (50), onwhich with an offset to the rear the cap magazines (3, 3A) are mounted.14. Spot welding cap changer according to claim 13, characterized inthat the access openings (40) of the cap magazines (3, 3A) are directedtowards and salient on different sides of the mounting plate (50),respectively.
 15. Spot welding cap changer according to claim 13,characterized in that the mounting plate (50) is supported and movablyguided on a support rail (5) which is mounted on a robot arm or firmlyinstalled.
 16. Spot welding cap changer according to claim 1,characterized in that sensors are arranged at the cap magazines (3, 3A),which send a signal to a control device when a predetermined remainingquantity of spot welding caps (K) is in stock in the respective capcarrier (31).